Field of the Invention
The present invention relates to xylanase variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
Description of the Related Art
Lignocellulose, the world's largest renewable biomass resource, is composed mainly of lignin, cellulose, and hemicellulose, of which a large part of the latter is xylan. Xylan is a polysaccharide formed from 1,4-β-glycoside-linked D-xylopyranoses. Xylanases (e.g., endo-1,4-beta-xylanase, EC 3.2.1.8) hydrolyze internal β-1,4-xylosidic linkages in xylan to produce smaller molecular weight xylose and xylo-oligomers.
Cellulose is a polymer of the simple glucose covalently linked by beta-1,4-bonds. Many microorganisms produce enzymes that hydrolyze beta-linked glucans. These enzymes include endoglucanases, cellobiohydrolases, and beta-glucosidases. Endoglucanases digest the cellulose polymer at random locations, opening it to attack by cellobiohydrolases. Cellobiohydrolases sequentially release molecules of cellobiose from the ends of the cellulose polymer. Cellobiose is a water-soluble beta-1,4-linked dimer of glucose. Beta-glucosidases hydrolyze cellobiose to glucose. Once the cellulose is converted to glucose, the glucose can be fermented by yeast into ethanol.
The conversion of lignocellulosic feedstocks into ethanol has the advantages of the ready availability of large amounts of feedstock, the desirability of avoiding burning or land filling the materials, and the cleanliness of the ethanol fuel. Wood, agricultural residues, herbaceous crops, and municipal solid wastes have been considered as feedstocks for ethanol production. These materials primarily consist of cellulose, hemicellulose, and lignin. Once the cellulose is converted to glucose, the glucose is easily fermented by yeast into ethanol.
There is a need in the art for xylanases with increased thermostability as a component of enzyme compositions for use in the degradation of lignocellulose at high temperatures.
The present invention provides xylanase variants with increased thermostability.